The present invention relates to a crystalline film of composite oxide and its production method and an amorphous film of composite oxide and its production method which are to be used as an electrode in a flat panel display or the like, as well as to a sintered compact of composite oxide to be used in producing the foregoing oxide films.
An ITO (Indium Tin Oxide) film is characterized in low resistivity and high transmission factor, and can be micro-fabricated easily. Since these characteristics are superior in comparison to other transparent conductive films, an ITO film is being broadly used in various fields including for use as a display electrode in a flat panel display. The deposition method of the ITO film in today's industrial production process is mostly based on the so-called sputter deposition method of performing sputtering using an ITO sintered compact as the target since the ITO film can be uniformly formed on a large area with favorable productivity.
In a flat panel display manufacturing process using an ITO transparent conductive film, the crystallinity of the ITO film immediately after the sputtering is amorphous, and, in most cases, micro-fabrication such as etching is performed with the ITO film in an amorphous state, and thermal annealing is subsequently performed to crystallize the ITO film. This is because an ITO amorphous film is advantageous in terms of productivity in a large etching rate, and the ITO crystal film is superior in low resistivity and in heat resistance, and both advantages can thereby be enjoyed.
Although most of the film obtained by sputtering the ITO target is amorphous, in many cases a part of the film becomes crystallized. The reason for this is that some particles that adhere to the substrate due to sputtering have a high energy level, the temperature of the film becomes so high as to exceed the crystallization temperature due to the transfer of energy after the particles adhere to the substrate, and a part of the film consequently becomes crystallized, although the crystallization temperature of the ITO film is approximately 150° C. and most of the film is amorphous since it will be lower than 150° C.
If a part of the ITO film becomes crystallized as described above, such crystallized portion will remain as so-called etching residue in the subsequent etching process, and cause problems such as a short circuit, since the etching rate of that part will be lower than that of an amorphous portion by roughly two orders of magnitude.
In light of the above, it is known that the addition of water (H2O) in addition to sputter gas such as argon in a chamber during sputtering is effective as a method of preventing the crystallization of the sputtered film and amorphizing the entire sputtered film (for example, refer to Thin Solid Films 445 (2003) p 235 to 240).
Nevertheless, the method of attempting to obtain an amorphous film by sputtering upon adding water entails numerous problems. Foremost, in many cases particles are generated on the sputtered film. These particles have an adverse effect on the flatness and crystallinity of the sputtered film. Since particles will not be generated if water is not added, the problem of generation of particles is caused by adding water.
In addition, even if the water concentration in the sputtering chamber is initially an adequate water concentration, the concentration will gradually fall below the adequate concentration, and a part of the sputtered film will become crystallized, since it gradually decreases pursuant to the lapse of the sputtering time.
On the other hand, however, if the concentration of the water to be added is increased in order to reliably obtain an amorphous sputtered film, the crystallization temperature upon crystallizing the film in the subsequent annealing process will become extremely high, which is a problem in that the resistivity of the obtained film will become extremely high.
In other words, if sputtering is performed upon adding water to amorphize the entire sputtered film, it is necessary to constantly monitor and control the water concentration within the chamber; however, this is extremely difficult and requires considerable time and effort.
In order to overcome the foregoing problems, a transparent conductive material as a stable amorphous material is sometimes used in substitute for an ITO film in which a crystalline film can be easily formed. For instance, with a sintered compact having a composition of adding zinc to indium oxide as the target, it is known that such a target can be sputtered to obtain an amorphous film, but the sputtered film obtained as described above is an extremely stable amorphous material and will not crystallize unless it is subject to a high temperature of 500° C. or higher.
Thus, it is not possible to attain the advantages in the production process of crystallizing the film and incomparably reducing the etching rate, and the resistivity of the sputtered film will be approximately 0.45 Ωcm, which is higher than the crystallized ITO film. Moreover, the visible light average transmission factor of this film is roughly 85%, and is inferior to an ITO film.
Also, the following patent documents and the like that are similar to the present invention in certain respects as a matter of form but different in terms of configuration and technical concept, and the outline thereof is explained below.
JP Patent Laid-Open Publication No. 2003-105532 and JP Patent Laid-Open Publication No. 2004-149883 describe a sputtering target for forming a transparent conductive film with high resistivity by adding insulating oxide to ITO, and calcium oxide, magnesium oxide and the like are listed as examples of the insulating oxide; however, the Examples provide a description regarding only silicon oxide. The object of these Patent Documents is only to obtain a high resistivity film, and does not contain any perspective based on the technical concept on the crystallinity of the film during deposition or the crystallization of the film based on the subsequent annealing process.
As described above, the conventional technology which uses a sintered compact having a composition of adding zinc to indium oxide as the target is insufficient as a solution since it has drawbacks such as the film resistivity being high.
Moreover, the patent documents and the like that are similar to the present invention in certain respects as a matter of form such as including descriptions of adding calcium to ITO do not give consideration to the problems that are indicated by the present invention, and simply aim to achieve the high resistivity of the film by adding calcium and the like. Thus, the foregoing patent documents and the like do not include the technical concept of controlling the crystallinity of the film or leveraging the low resistivity of the crystallized film as with the present invention.
In addition, if the effect of high resistivity is to be sought based on the concentration of the added calcium and the like, the additive amount is too high, and there are no descriptions on favorable film characteristics of the present invention or descriptions in the Examples regarding the production method and the like.